Composite carbon foam

ABSTRACT

A composite foam including a carbon foam material comprising a network of pores and a plurality of discontinuities and a secondary material deposited on at least some of the plurality of discontinuities of the carbon foam material.

TECHNICAL FIELD

The present invention relates to composite materials and, moreparticularly, to an electrically-conductive composite carbon foam.

BACKGROUND

Electrochemical batteries, including, for example, lead acid andnickel-based batteries, among others, are known to include at least onepositive current collector, at least one negative current collector, andan electrolytic solution. In traditional lead acid batteries, forexample, both the positive and negative current collectors areconstructed from lead. The role of these lead current collectors is totransfer electric current to and from the battery terminals during thedischarge and charging processes. Storage and release of electricalenergy in lead acid batteries is enabled by chemical reactions thatoccur in a paste disposed on the current collectors. The positive andnegative current collectors, once coated with this paste, are referredto as positive and negative plates, respectively. A notable limitationon the durability of lead-acid batteries is corrosion of the leadcurrent collector of the positive plate.

The rate of corrosion of the lead current collector is a major factor indetermining the life of the lead acid battery. Once the electrolyte(e.g., sulfuric acid) is added to the battery and the battery ischarged, the current collector of each positive plate is continuallysubjected to corrosion due to its exposure to sulfuric acid and to theanodic potentials of the positive plate. One of the most damagingeffects of this corrosion of the positive plate current collector isvolume expansion. Particularly, as the lead current collector corrodes,lead dioxide is formed from the lead source metal of the currentcollector. Moreover, this lead dioxide corrosion product has a greatervolume than the lead source material consumed to create the leaddioxide. Corrosion of the lead source material and the ensuing increasein volume of the lead dioxide corrosion product is known as volumeexpansion.

Volume expansion induces mechanical stresses on the current collectorthat deform and stretch the current collector. At a total volumeincrease of the current collector of approximately 4 percent to 7percent, the current collector may fracture. As a result, batterycapacity may drop, and eventually, the battery will reach the end of itsservice life. Additionally, at advanced stages of corrosion, internalshorting within the current collector and rupture of the cell case mayoccur. Both of these corrosion effects may lead to failure of one ormore of the cells within the battery.

One method of extending the service life of a lead acid battery is toincrease the corrosion resistance of the current collector of thepositive plate. Several methods have been proposed for inhibiting thecorrosion process in lead acid batteries. Because carbon does notoxidize at the temperatures at which lead-acid batteries generallyoperate, some of these methods have involved using carbon in variousforms to slow or prevent the detrimental corrosion process in lead acidbatteries. For example, in U.S. Patent Publication No. 20040121238carbon foam has been proposed as a current collector material for use inlead acid batteries. Use of carbon foam (e.g., graphite foam) as acurrent collector can increase the corrosion resistance and surface areaof the current collector over lead current collector grids. Thisadditional surface area of the current collectors may increase thespecific energy and power of the battery, thereby enhancing itsperformance. However, among the network of pores formed in the foam,there may exist a plurality of discontinuities that may allowintercalation of electrically charged ions into the structure of thefoam. These ions can act like a wedge being driven within the carbonfoam structure causing internal damage (e.g., cracking and separation)and leading to premature failure of the current collector. The effectsof intercalation may be particularly prevalent when the carbon foamstructure includes graphite. Further, discontinuities can providereaction sites that promote chemical interaction between the carbon foamand various chemically reactive species. This chemical interaction cancompromise the structural integrity of the carbon foam. The chemicalreactivity may have destructive effects on many types of carbon foams.

The present invention is directed to overcoming one or more of theproblems or disadvantages existing in the prior art.

SUMMARY OF THE INVENTION

Apparatus and methods of the present invention relate to an electricallyconductive composite carbon foam.

One embodiment of the disclosure includes a composite foam. Thecomposite foam includes a carbon foam material including a network ofpores and a plurality of discontinuities. The composite foam furtherincludes a secondary material selectively deposited on or within atleast some of the plurality of discontinuities of the carbon foammaterial in an amount between about 0.5 percent by weight or greater andless than 25 percent by weight of the composite foam.

In another embodiment, an electrically conductive composite foam isdisclosed. The electrically conductive composite foam includes a carbonfoam material including a network of pores and a plurality ofdiscontinuities, wherein the carbon foam has a resistivity value nogreater than 50,000 micro ohm-cm. The electrically conductive compositefoam further includes a secondary material selectively deposited on atleast some of the plurality of discontinuities of the carbon foammaterial.

In yet another embodiment, a lead acid battery is disclosed. The leadacid battery includes a housing, at least one cell disposed within thehousing, an electrolyte, and at least one electrically conductivecomponent including a composite foam material. The composite foammaterial includes a carbon foam material comprising a network of poresand a plurality of discontinuities and a secondary material deposited onor within at least some of the plurality of discontinuities of thecarbon foam material.

In yet another embodiment, a method for producing a composite foam isdisclosed. The method includes the step of providing a treatmentmixture, including a secondary material and a substantially polarsolvent, wherein the secondary material maintains an electrical chargeof a first polarity. The method further includes the steps of exposing acarbon foam material, including a network of pores and a plurality ofdiscontinuities, to the treatment mixture, and applying a voltagepotential of a second polarity to the carbon foam material, wherein thesecond polarity is opposite to the first polarity.

In yet another embodiment, a method for reinforcing a composite foamcomponent is disclosed. The method includes the steps of providing atreatment mixture comprising a secondary material and a solvent andexposing a carbon foam material comprising a network of pores and aplurality of discontinuities to the treatment mixture, wherein exposingthe carbon foam material to the treatment mixture effects a transfer ofat least some of the secondary material to the carbon foam material suchthat the secondary material is selectively deposited on or within atleast some of the plurality of discontinuities in an amount of about 0.5percent by weight or greater and less than 25 percent by weight of thecomposite foam.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description, serve to explain the principles of theinvention. In the drawings:

FIG. 1 illustrates a battery 10 in accordance with an exemplaryembodiment of the present invention;

FIG. 2A illustrates a current collector 20 according to an exemplaryembodiment of the present invention;

FIG. 2B illustrates a closer view of tab 21, which optionally may beformed on current collector 20;

FIG. 3 provides a two-dimensional representation, at approximately 100×magnification, of an exemplary carbon foam;

FIG. 4 is a flow diagram depicting an exemplary method for treating acarbon foam with a secondary material consistent with an embodiment ofthe present invention; and

FIG. 5 is a flow diagram depicting another exemplary method for treatinga carbon foam with a secondary material consistent with an embodiment ofthe present invention.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to exemplary embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 1 illustrates a battery 10 in accordance with an exemplaryembodiment of the present invention. Battery 10 includes a housing 11and terminals 12, which may be external to housing 11. At least one cell13, is disposed within housing 11. Battery 10 may operate with a singlecell 13, or alternatively, multiple cells may be connected in series orin parallel to provide a desired total potential of battery 10.

Each cell 13 may be composed of alternating positive and negative platesor electrodes immersed in an electrolytic solution. The electrolyticsolution composition may be chosen to correspond with a particularbattery chemistry. For example, lead acid batteries may include anacidic electrolytic solution. Any suitable acid may be used to providethe electrolyte of a lead acid battery. In one particular embodiment,sulfuric acid may be mixed with water to provide the electrolytesolution of battery 10. Alternatively, batteries of other chemistriesmay include other electrolytes. For example, nickel-based batteries mayinclude alkaline electrolyte solutions that include a base (e.g., KOH)mixed with water.

Battery 10 further includes at least one electrically conductivecomponent including, for example, current collectors, bus bars, and anyother electrically conductive component consistent with the presentinvention. In one embodiment, the positive and negative plates of eachcell 13 may include an electrically conductive current collector packedor coated with a chemically active material. The composition of thechemically active material may depend on the chemistry of battery 10.For example, lead acid batteries may include a chemically activematerial including, for example, an oxide or salt of lead. Further, theanode plates (i.e., positive plates) of nickel cadmium (NiCd) batteriesmay include cadmium hydroxide (Cd(OH)₂) material; nickel metal hydridebatteries may include lanthanum nickel (LaNi₅) material; nickel zinc(NiZn) batteries may include zinc hydroxide (Zn(OH)₂) material; andnickel iron (NiFe) batteries may include iron hydroxide (Fe(OH)₂)material. In all of the nickel-based batteries, the chemically activematerial on the cathode (i.e., negative) plate may be nickel hydroxide.

FIG. 2A illustrates a current collector 20 according to an exemplaryembodiment of the present invention. Current collector 20 may include athin, rectangular body and a tab 21 used to form an electricalconnection with current collector 20. Tab 21, however, may be omitted insome embodiments.

The current collector shown in FIG. 2A may be used to form either apositive or a negative plate. As previously stated, chemical reactionsin the active material disposed on the current collectors of the batteryenable storage and release of energy. The composition of this activematerial, and not the current collector material, determines whether agiven current collector functions as either a positive or a negativeplate.

While the type of plate, whether positive or negative, does not dependon the material selected for current collector 20, the current collectormaterial and configuration can affect the characteristics andperformance of battery 10. For example, during the charging anddischarging processes, each current collector 20 transfers the resultingelectric current to and from battery terminals 12. In order toefficiently transfer current to and from terminals 12, current collector20 may be formed from a conductive material. Further, the susceptibilityof the current collector material to corrosion may affect not only theperformance of battery 10, but it can also impact the service life ofbattery 10. In addition to the material selected for the currentcollector 20, the configuration of current collector 20 can also beimportant to battery performance. For instance, the amount of surfacearea available on current collector 20 may influence the specificenergy, specific power, and the charge/discharge rates of battery 10.

In an exemplary embodiment of the present invention, current collector20, as shown in FIG. 2A, is formed from a carbon foam material, whichmay include carbon or carbon-based materials that exhibit some degree ofporosity. In certain embodiments, the carbon may include graphite foam.Because the foam is carbon, it can resist corrosion even when exposed toelectrolytes and to the electrical potentials of the positive ornegative plates. Further, current collectors composed of carbon foam mayexhibit more than 2000 times the amount of surface area provided byconventional current collectors.

The disclosed foam material may include any carbon-based materialincluding a three-dimensional network of struts and pores. The foam maycomprise either or both of naturally occurring and artificially derivedmaterials.

FIG. 2B illustrates a closer view of tab 21, which optionally may beformed on current collector 20. Tab 21 may be coated with a conductivematerial and used to form an electrical connection with the currentcollector 20. In addition to tab 21, other suitable configurations forestablishing electrical connections with current collector 20 may beused. The conductive material used to coat tab 21 may include a metalthat is more conductive than the carbon foam current collector. Coatingtab 21 with a conductive material may provide structural support for tab21 and create a suitable electrical connection capable of handling thehigh currents present in a lead acid and nickel-based batteries.

FIG. 3 provides a two-dimensional representation, at approximately 100×magnification, of an exemplary carbon foam. The carbon foam may includea network of pores 41. These pores provide a large amount of surfacearea for each current collector 20. The carbon foam may further includediscontinuities 43. The term “discontinuity” as used herein shall beunderstood to mean any openings, cracks, steps, fissures, separations,chasms, apertures, or perforations within the solid structure of thecarbon foam material. Discontinuities may be readily apparent orsubstantially indiscernible when viewed with the naked eye or under amicroscope. Further, discontinuities may vary in size, shape, andstructure. For example, a discontinuity may include a hairline crack onthe walls of a pore or a chasm-like separation between sheets ofgraphite within the foam, among others.

In one embodiment, the carbon foam may include from about 4 to about 50pores per centimeter and an average pore size of at least about 200micrometers. In other embodiments, however, the average pore size may besmaller. For example, in certain embodiments, the average pore size maybe at least about 40 micrometers. In still other embodiments, theaverage pore size may be at least about 20 micrometers. While reducingthe average pore size of the carbon foam material may have the effect ofincreasing the effective surface area of the material, average poresizes below 20 micrometers may impede or prevent penetration of thechemically active material into pores of the carbon foam material.

Regardless of the average pore size, a total porosity value for thecarbon foam may be at least 60 percent. In other words, at least 60percent of the volume of the carbon foam structure may be includedwithin pores 41. Carbon foam materials may also have total porosityvalues less than 60 percent. For example, in certain embodiments, thecarbon foam may have a total porosity value of at least 30 percent.

Moreover, the carbon foam may have an open porosity value of at least 90percent. Therefore, at least 90 percent of pores 41 are open to adjacentpores such that the network of pores 41 forms a substantially opennetwork. This open network of pores 41 may allow the active materialdeposited on each current collector 20 to penetrate within the carbonfoam structure. In addition to the network of pores 41, the carbon foamincludes a web of structural elements 42 that provide support for thecarbon foam. In total, the network of pores 41 and the structuralelements 42 of the carbon foam may result in a density of less thanabout 0.6 gm/cm³ for the carbon foam material.

Due to the conductivity of the carbon foam of the present invention,current collectors 20 can efficiently transfer current to and frombattery terminals 12, or any other conductive elements providing accessto the electrical potential of battery 10. In certain forms, theuntreated carbon foam may offer sheet resistivity values of less thanabout 1 ohm-cm. In still other forms, the untreated carbon foam may havesheet resistivity values of less than about 0.75 ohm-cm.

In one embodiment, the carbon foam may be a graphite foam used to formcurrent collector 20. One such graphite foam, under the trade namePocoFoam™, is available from Poco Graphite, Inc. The density and porestructure of graphite foam may be similar to carbon foam. A primarydifference between graphite foam and carbon foam is the orientation ofthe carbon atoms that make up the structural elements 42. For example,in carbon foam, the carbon may be at least partially amorphous. Ingraphite foam, however, more of the carbon is ordered into a graphite,layered structure. Because of the ordered nature of the graphitestructure, graphite foam may offer higher conductivity than carbon foam.Untreated graphite foam may exhibit electrical resistivity values ofbetween about 100 micro-ohm-cm and about 2,500 micro-ohm-cm. In somecases, graphite foams may approach resistivity values up to 50,000micro-ohm-cm.

The carbon and graphite foams of the present invention may also beobtained by subjecting various organic materials to a carbonizing and/orgraphitizing process. In one exemplary embodiment, various wood speciesmay be carbonized and/or graphitized to yield the carbon foam materialfor current collector 20. Wood includes a natural occurring network ofpores. These pores may be elongated and linearly oriented. Moreover, asa result of their water-carrying properties, the pores in wood form asubstantially open structure. Certain wood species may offer an openporosity value of at least about 90 percent. The average pore size ofwood may vary among different wood species, but in an exemplaryembodiment of the invention, the wood used to form the carbon foammaterial has an average pore size of at least about 20 microns.

Many species of wood may be used to form the carbon foam of theinvention. As a general class, most hardwoods have pore structuressuitable for use in the carbon foam current collectors of the invention.Optionally, the wood selected for use in creating the carbon foam mayoriginate from tropical growing areas. For example, unlike wood grown inclimates with significant seasonal variation, wood from tropical regionsmay have a less defined growth ring structure. As a result, the porousnetwork of wood from tropical areas may lack certain non-uniformitiesthat can result from the presence of growth rings. Exemplary woodspecies that may be used to create the carbon foam include oak,mahogany, teak, hickory, elm, sassafras, bubinga, palms, and many othertypes of wood.

To provide the carbon foam, wood may be subjected to a carbonizationprocess to create carbonized wood (e.g., a carbon foam material). Forexample, heating of the wood to a temperature of between about 800degrees C. and about 1400 degrees C. may have the effect of expellingvolatile components from the wood. The wood may be maintained in thistemperature range for a time sufficient to convert at least a portion ofthe wood to a carbon matrix. This carbonized wood will include theoriginal porous structure of the wood. As a result of its carbon matrix,however, the carbonized wood can be electrically conductive andresistant to corrosion. During the carbonization process, the wood maybe heated and cooled at any desired rate. In one embodiment, however,the wood may be heated and cooled sufficiently slowly to minimize orprevent cracking of the wood/carbonized wood. Also, heating of the woodmay occur in an inert environment.

The carbonized wood may be used to form current collectors 20 withoutadditional processing. Optionally, however, the carbonized wood may besubjected to a graphitization process to create graphitized wood (e.g.,a graphite foam material). Graphitized wood is carbonized wood in whichat least a portion of the carbon matrix has been converted to a graphitematrix. As previously noted, the graphite structure may exhibitincreased electrical conductivity as compared to non-graphite carbonstructures. Graphitizing the carbonized wood may be accomplished byheating the carbonized wood to a temperature of between about 2400degrees C. and about 3000 degrees C. for a time sufficient to convert atleast a portion of the carbon matrix of the carbonized wood to agraphite matrix. Heating and cooling of the carbonized wood may proceedat any desired rate. In one embodiment, however, the carbonized wood maybe heated and cooled sufficiently slowly to minimize or preventcracking. Also, heating of the carbonized wood may occur in an inertenvironment.

Discontinuities 43 may be of variable shapes and sizes and exist atnumerous areas and at random intervals throughout the carbon foamstructure. Discontinuities 43 may allow intercalation of electricallycharged ions and may also create multiple reactive sites on a carbonfoam structure for chemical attack, among other things. Particularly, anuntreated graphite foam may experience destructive intercalation ofelectrically charged ions via discontinuities 43 when exposed to certainchemical environments (e.g., those present in a lead-acid battery) andabsent any treatment of discontinuities 43. For example, when coatedwith an active material and utilized as a current collector in abattery, the untreated graphite foam structure may experience forcesmuch like a wedge driving the layered graphite structure apart. Theelectrically charged nature of the current collector attracts the ionsand causes them to be drawn deeper inside discontinuities 43 causingfurther damage.

Additionally, surfaces of discontinuities 43 provide a large number ofreactive areas whereby reactive chemicals may work to break downunderlying carbon structure. Such forces may cause additional crackingresulting in an increase in discontinuities 43 thereby leading toadditional chemically reactive sites and, in the case of graphite,additional intercalation. Ultimately, these forces may eventually leadto complete destruction of the conductive path through the foam, whichcan mark the failure of a current collector.

To minimize intercalation, reduce reactive area, and/or add additionalstructural reinforcement to an electrically conductive carbon foam,treatment with a secondary material may be performed, resulting in acomposite carbon foam. For example, a secondary material may bedeposited on a carbon foam structure, particularly on and arounddiscontinuities 43, to substantially close, or limit the open areaassociated with discontinuities 43. By concentrating the secondarymaterial on and around discontinuities 43, discontinuities 43 may becomesubstantially covered or sealed, thereby creating physical restraint andimpeding intercalation of the charged ions while also reducing theavailable reactive area. The remaining surface area of the carbon foam(e.g., including areas with few or no discontinuities) may remainsubstantially uncovered by the secondary material. Becausediscontinuities 43 may also create areas of concentrated physicalstress, providing additional support in such areas may also have thebeneficial effect of enhancing the structural integrity of the carbonfoam.

In one embodiment consistent with the present invention, the secondarymaterial used for treatment of a carbon foam may include non-conductivematerials such as polymers and glasses. For example, the secondarymaterial may include a polymer such as polyvinylalanine orpolycarbonates. However, the secondary material may include any suitablepolymer such as, for example, polyethylene, polypropylene, polystyrene,Teflon, urethane, polyesters, polyvinylpyrollidone, polyvinylchloride,or any other suitable thermoplastic or thermoset material known in theart. In another embodiment, the secondary material may include, forexample, a phosphate glass, a silicate glass, or other similarly derivedmaterial. One of skill in the art will recognize that numerous othersuitable materials may also be used as a secondary material whileremaining within the scope of the invention.

In one example consistent with the present invention, a secondarymaterial may be deposited on a carbon foam structure in an amount ofabout 0.5 percent by weight or greater and less than 25 percent byweight of the composite foam. In such an embodiment, and using treatmentmethods discussed in greater detail with reference to FIGS. 4 and 5, thesecondary material may be concentrated on discontinuities 43. Surfacesof structural elements 42 and pores 41 of the carbon foam may remainsubstantially free of secondary material while discontinuities 43 may besubstantially covered. In such an embodiment, the weight increase of thecomposite foam can be minimized, which may provide beneficial energy toweight ratio when the foam is utilized within a lead acid battery.

FIG. 4 is a flow diagram depicting an exemplary method for treating acarbon foam with a secondary material. To apply a secondary material toa carbon foam structure, a treatment mixture suitable for exposing thecarbon foam to the secondary material may be prepared (step 50). Theterm “mixture” as used herein may encompass any combination of a solventand secondary materials (solids or liquids) resulting in a slurry,solution, emulsion, suspension, or colloidal preparation. The resultingcombination (mixture) may be distributed over the surfaces, pores, anddiscontinuities of a porous and irregularly shaped structure. The term“solvent” as used herein is intended to refer to the portion of any suchmixture into which the secondary material is introduced.

Prior to creating a treatment mixture, initial preparation of asecondary material may be performed. For example, in an embodiment wherethe secondary material is obtained in solid form (e.g., a block), somemechanical crushing or grinding of the material may initially beperformed to place the secondary material in a powder-like or granularstate. One of skill in the art will recognize that other methods forpreparing a secondary material may be used without departing from thescope of the present invention. For example, where a secondary materialis obtained in sheets, cutting and/or grinding of the sheets into piecesof a desired size may be performed.

Once the secondary material has been prepared, the secondary materialmay be added to a solvent in a quantity between about 0.05 percent to 25percent by weight of the mixture. In one embodiment, the secondarymaterial may be added to the solvent in a quantity between about 0.1percent to 0.5 percent by weight of the mixture. The resulting treatmentmixture may be agitated, stirred, or may be left to combine on its ownbased on the materials and solvents used as well as time constraints. Inone embodiment, the solvent may include a polar solvent such as water.The use of a polar solvent may cause particles of a secondary materialto acquire a charge through frictional or other interaction with thepolar solvent. This can be useful when applying a voltage potentialintended to induce an opposite charge on a carbon foam material for thepurposes of attracting secondary material particles. In otherembodiments consistent with the present invention, the solvent may alsoinclude acetic acid, ammonia, and methanol. One of skill in the art willrecognize that other polar solvents may be used without departing fromthe scope of the present invention.

By adding the secondary material to a polar solvent, particles of thesecondary material may develop an electrical charge on their surface.The charge developed by these particles may cause like particles ofsecondary material to repel one another. This charge may also allow theparticles to remain “suspended” in the mixture. The charge developed bythe particles of secondary material may be positive or negative and maydepend on the polar solvent used as well as the secondary materialitself. For example, when materials including polycarbonates,polyvinylalanine, and epoxies are combined with water, the particles ofsecondary material may develop a positive charge. Alternatively, asurfactant (e.g., Darvon-C or methyl methacrylate) may be added to sucha treatment mixture, which may cause the same positively chargedparticles of secondary material to become surrounded with a negativecharge as a result of the surfactant's presence. Other secondarymaterials may also develop a negative charge when combined with water inthe absence of a surfactant. For example, particles of secondarymaterials including silicates may develop a negative charge whencombined with water.

Once the treatment mixture has been prepared, a carbon foam structuremay be exposed to the treatment mixture (step 52). In one embodiment,exposure to the treatment mixture may include immersing the carbon foamstructure in the mixture such that the entire structure, including pores41, structural elements 42, and discontinuities 43, may be exposed tothe treatment mixture. In such an embodiment, the treatment mixture maybe allowed to substantially penetrate the pores 41 and discontinuities43 present on the carbon foam structure. Alternatively, the carbon foamstructure may not be completely immersed but may be bathed in thetreatment mixture while maintaining at least a portion of the carbonfoam structure above the level of the mixture. One of skill in the artwill recognize that many other methods for exposing the carbon foamstructure to the treatment mixture may be used. For example, a treatmentmixture may be sprayed on, dripped on, shaken on, painted on,electrostatically applied, etc.

While the carbon foam structure is exposed to the treatment mixture, avoltage potential having a polarity opposite to the surface chargeacquired by the particles of secondary material in the treatment mixturemay be applied to the carbon foam structure (step 54). In response tothe applied voltage, the edges of discontinuities 43 present within thefoam may exhibit current densities higher than the surrounding foamstructure. This is because a discontinuity causes current to flow aroundits edges due to the broken conductive path that would normally exist inthe absence of the discontinuity. This flow causes a concentration ofcurrent along the edges of a discontinuity and a reduction in thecurrent density at other areas lying further from the discontinuity.Such a concentration of current surrounding a discontinuity can resultin a substantially higher number of the charged secondary materialparticles being drawn to and deposited on discontinuities 43 withrelatively fewer particles being deposited on the remaining surfaces ofstructural elements 42 of the carbon foam structure.

Application of a non-conductive secondary material consistent with anembodiment of the present invention may be self-limiting. That is,deposition of the secondary material on discontinuities 43 and thecarbon foam structure may reduce associated current densities therebyreducing the attractive forces between the carbon foam structure and thecharged particles of secondary material. Further, as particles ofsecondary material are pulled out of the treatment mixture, fewerparticles within the treatment mixture may be available for deposition.The amount of secondary material deposited on the carbon foam structuremay be related to of the duration of the applied voltage, the magnitudeof the applied voltage, the amount of secondary material in thetreatment mixture, the transport properties of the treatment mixture,the number and density of discontinuities 43, and the surface area ofthe carbon foam structure. In certain embodiments, a voltage less thanabout 5 V (and preferably between 50 mV and about 1.4 V) may be appliedto the foam to deposit secondary material substantially on and arounddiscontinuities 43. The duration of the voltage application may varydepending on the surface area of the foam and the coverage desired.Where additional coverage of a particular carbon foam structure with asecondary material is desired, the voltage may be applied for longerdurations and/or additional secondary material may be added to thetreatment mixture. Conversely, shorter durations of applied voltageand/or less secondary material in the treatment mixture may be usedwhere less coverage is desired.

Once the secondary material has been deposited on the carbon foamstructure in a desired amount, the structure may be removed from thetreatment mixture and cured (step 56). The need for curing may depend onthe particular secondary material selected. For example, an epoxy basedsecondary material or thermoset polymer may require curing whereas othersecondary materials may require minimal or no curing. The term “cure” asused herein is meant to encompass any process whereby a secondarymaterial undergoes a process (physical, chemical, or combinationthereof) resulting in a final state and/or shape of the materialdifferent from that existing after deposition but before the process.

Curing may involve a heat treatment applied to the carbon foam structureand the secondary material. For example, where a thermoplastic polymerhas been selected as the secondary material, heat treatment may involveheating the carbon foam structure (and deposited secondary material) tobetween about 90 degrees C. and about 300 degrees C. and holding at thattemperature for between about 1 to 10 minutes. The thermoplastic polymerwhen heated may soften, melt, or liquefy thereby allowing the polymer toflow into and around discontinuities 43 in the carbon foam. Upon coolingof the polymer, it may harden in a different shape (due to flow or otherfactors) and may adhere to the underlying carbon foam structureresulting in a composite carbon foam structure with substantiallycovered discontinuities and additional structural support. In anotherembodiment, a glass may be selected as the secondary material. When aglass has been selected as the secondary material, heat treatment mayinvolve heating the carbon foam structure (and deposited secondarymaterial) to between about 180 degrees C. and about 800 degrees C. andholding at that temperature for between about 2 to 6 hours. One ofordinary skill in the art will recognize that curing temperatures anddurations may be substantially dependent on the secondary material used.

Curing may also involve exposing the carbon foam structure and secondarymaterial to a reactant. For example, an epoxy based secondary materialdeposited on a carbon foam may be exposed to a substance designed toeffect a hardening of the epoxy. Such exposure may cause the epoxy toundergo a chemical reaction and harden, substantially covering andadhering to discontinuities 43. Exposure to a reactant may be performedthrough numerous methods, for example, spraying or painting the reactanton to the carbon foam structure and secondary material.

FIG. 5 is a flow diagram depicting another exemplary method for treatinga carbon foam with a secondary material. Prior to treating the carbonfoam structure with a secondary material, a treatment mixture suitablefor exposing the carbon foam to the secondary material may be prepared(step 60).

Prior to creating a treatment mixture, initial preparation of asecondary material may be performed. For example, in an embodiment wherethe secondary material is obtained in solid form (e.g., a block), somemechanical crushing or grinding of the material may initially beperformed to place the secondary material in a powder-like or granularstate. One of skill in the art will recognize that other methods forpreparing a secondary material may be used without departing from thescope of the present invention. For example, where a secondary materialis obtained in sheets, cutting and/or grinding of the sheets into piecesof a desired size may be performed.

Following preparation of a secondary material, a quantity of theprepared secondary material between about 1 percent and 10 percent byweight of the resulting mixture may be added to a substantiallynon-polar solvent to form a treatment mixture. In one embodiment, theprepared secondary material may be added to the solvent in a quantitybetween about 4 percent and 6 percent by weight of the resultingmixture. Examples of substantially non-polar solvents may include,xylene, methylene chloride, benzene, ketones, and acetone. One of skillin the art will recognize that numerous other substantially non-polarsolvents may be used without departing from the scope of the presentinvention. Once the secondary material has been added to the non-polarsolvent, the mixture may or may not be agitated as desired to produce aprepared treatment mixture.

Following preparation of the treatment mixture, a carbon foam structuremay be exposed to the mixture (step 62). Exposure to the mixture mayinclude “wash-coating” or immersing the carbon foam structure in themixture such that the entire structure is exposed to the mixturefollowed by removing the carbon foam structure from the mixture. In suchan embodiment, the treatment mixture may be allowed to substantiallypenetrate pores 41 and discontinuities 43 present on the carbon foamstructure. Alternatively, the carbon foam structure may be partiallyimmersed in the mixture such that a portion of the structure remainsabove the level of the mixture. One of skill in the art will recognizethat other methods for exposing the carbon foam structure to thetreatment mixture may be used. For example, a treatment mixture may besprayed on, dripped on, shaken on, painted on, etc.

During exposure to the mixture, capillary action associated withdiscontinuities present on the carbon foam structure may cause largeramounts of the mixture (and secondary material) to be drawn near andinto discontinuities 43. This capillary action may promote coverage ofdiscontinuities 43, while minimizing coverage of the surroundingsurfaces of structural elements 42. Further, it may be possible tocontrol the amount of secondary material deposited on the carbon foamand discontinuities therein, by varying the time of exposure to thetreatment mixture. For example, a carbon foam structure exposed to amixture containing secondary material in an amount approximately 5percent by weight, may result in deposition of between about 0.5 percentand 25 percent of secondary material by weight of the resultingcomposite foam depending on the duration of exposure. Longer exposuremay yield greater amounts of secondary material deposited on the carbonfoam, whereas shorter exposure durations may result in smaller amounts.

Once the carbon foam structure has been removed from the mixture, theremaining solvent may be removed (e.g., evaporated) leaving thesecondary material behind on the composite carbon foam (step 64). In oneembodiment consistent with the present invention, volatility of asolvent may be increased, thereby enhancing evaporation, by placing thecomposite carbon foam in a vacuum or by applying heat to the structure.Heating the composite carbon foam may also perform the secondary processof curing (where desired). Alternatively, a solvent may be allowed toevaporate at a rate based on the standard atmospheric volatility of thesolvent. For example, xylene, a highly volatile solvent, may be used asthe solvent for the treatment mixture and may be allowed to evaporateunder standard atmospheric conditions following treatment. Less volatilesolvents may require additional measures to facilitate removal from thecomposite carbon foam. Further, other methods including, for example,chemical reactions or mechanical methods may be used for removing thesolvent from the composite carbon foam.

Following removal of the solvent, where desired, the secondary materialmay be cured. Curing may involve a heat treatment applied to the carbonfoam structure and the secondary material. For example, where athermoplastic polymer has been selected as the secondary material, heattreatment may involve heating the carbon foam structure (and depositedsecondary material) to between about 90 degrees C. and about 300 degreesC. and holding at that temperature for between about 1 to 10 minutes.The thermoplastic polymer when heated may soften, melt, or liquefythereby allowing the polymer to flow into and around discontinuities 43in the carbon foam. Upon cooling of the polymer, it may harden in adifferent shape (due to flow or other factors) and may adhere to theunderlying carbon foam structure resulting in a composite carbon foamstructure with substantially covered discontinuities and additionalstructural support. In another embodiment, a glass may be selected asthe secondary material. When a glass has been selected as the secondarymaterial, heat treatment may involve heating the carbon foam structure(and deposited secondary material) to between about 180 degrees C. andabout 800 degrees C. and holding at that temperature for between about 2to 6 hours. One of ordinary skill in the art will recognize that curingtemperatures and durations may be substantially dependent on thesecondary material used.

Curing may also involve exposing the carbon foam structure and secondarymaterial to a reactant. For example, an epoxy based secondary materialdeposited on a carbon foam may be exposed to a substance designed toeffect a hardening of the epoxy. Such exposure may cause the epoxy toundergo a chemical reaction and harden, substantially covering andadhering to discontinuities 43. Exposure to a reactant may be performedthrough numerous methods, for example, spraying or painting the reactanton to the carbon foam structure and secondary material.

Other materials not mentioned may be used in manufacturing componentsconsistent with the present invention and without departing from thescope and spirit of the invention.

It is intended that the specification and examples be considered asexemplary only, with a true scope and spirit of the invention beingindicated by the following claims.

1. A composite foam, comprising: a carbon foam material including anetwork of pores and a plurality of discontinuities; and a secondarymaterial selectively deposited on or within at least some of theplurality of discontinuities of the carbon foam material in an amountbetween about 0.5 percent by weight or greater and less than 25 percentby weight of the composite foam.
 2. The composite foam of claim 1,wherein the carbon foam material includes graphite foam.
 3. Thecomposite foam of claim 1, wherein the secondary material includes apolymer.
 4. The composite foam of claim 3, wherein the secondarymaterial includes a thermoplastic polymer.
 5. The composite foam ofclaim 3, wherein the polymer includes at least one of polyvinylalanine,polystyrene, and polycarbonate.
 6. The composite foam of claim 1,wherein the secondary material includes a glass.
 7. The composite foamof claim 6, wherein the secondary material includes at least one of aphosphate glass and a silicate glass.
 8. The composite foam of claim 1,wherein at least some surfaces of structural elements defining thenetwork of pores are substantially free of secondary material.
 9. Thecomposite foam of claim 1, wherein the composite foam has a resistivityvalue no greater than 50,000 micro-ohm-cm.
 10. The composite foam ofclaim 1, wherein the composite foam comprises wood.
 11. An electricallyconductive composite foam, comprising: a carbon foam material comprisinga network of pores and a plurality of discontinuities, wherein thecarbon foam has a resistivity value no greater than 50,000 micro-ohm-cm;and a secondary material selectively deposited on or within at leastsome of the plurality of discontinuities of the carbon foam material.12. The electrically conductive composite foam of claim 11, wherein thecarbon foam material includes graphite foam.
 13. The electricallyconductive composite foam of claim 11, wherein the secondary materialincludes a polymer.
 14. The electrically conductive composite foam ofclaim 13, wherein the secondary material includes a thermoplasticpolymer.
 15. The electrically conductive composite foam of claim 13,wherein the polymer includes at least one of polyvinylalanine,polystyrene, and polycarbonate.
 16. The electrically conductivecomposite foam of claim 11, wherein the secondary material includes aglass.
 17. The electrically conductive composite foam of claim 16,wherein the secondary material includes least one of a phosphate glassand a silicate glass.
 18. The electrically conductive composite foam ofclaim 11, wherein at least some surfaces of structural elements definingthe network of pores are substantially free of secondary material.
 19. Alead acid battery, comprising: a housing; at least one cell disposedwithin the housing; an electrolyte; and at least one electricallyconductive component including a composite foam material, comprising: acarbon foam material comprising a network of pores and a plurality ofdiscontinuities; and a secondary material deposited on at least some ofthe plurality of discontinuities of the carbon foam material.
 20. Thelead acid battery of claim 19, wherein the at least one electricallyconductive component comprises a current collector.
 21. The lead acidbattery of claim 20, further comprising a chemically active pastedisposed upon the composite foam material such that the chemicallyactive paste penetrates at least some of the pores of the carbon foammaterial.
 22. The lead acid battery of claim 19, wherein the electrolyteincludes an acidic solution.
 23. The lead acid battery of claim 22,wherein the acidic solution includes sulfuric acid.
 24. The lead acidbattery of claim 19, wherein the carbon foam material includes graphitefoam.
 25. The lead acid battery of claim 19, wherein the secondarymaterial is disposed on the composite foam material in an amount betweenabout 0.5 percent by weight and less than 25 percent by weight of thecomposite foam material.
 26. The lead acid battery of claim 19, whereinthe resistivity of the composite foam material is not greater than50,000 micro-ohm-cm.
 27. A method for producing a composite foam, themethod comprising: providing a treatment mixture, including a secondarymaterial and a substantially polar solvent, wherein the secondarymaterial maintains an electrical charge of a first polarity; exposing acarbon foam material, including a network of pores and a plurality ofdiscontinuities, to the treatment mixture; and applying a voltagepotential of a second polarity to the carbon foam material, wherein thesecond polarity is opposite to the first polarity.
 28. The method ofclaim 27, wherein the carbon foam material includes graphite foam. 29.The method of claim 27, wherein the substantially polar solvent includesat least one of water, ammonia, methanol, and acetic acid.
 30. Themethod of claim 27, wherein the first polarity is positive.
 31. Themethod of claim 27, wherein the first polarity is negative.
 32. Themethod of claim 27, wherein the secondary material includes a polymer.33. The method of claim 27, further comprising: following application ofthe second charge, curing the secondary material.
 34. The method ofclaim 32, wherein curing the secondary material includes heating thematerial to a predetermined temperature.
 35. The method of claim 32,wherein curing the secondary material includes exposing the secondarymaterial to a reactant.
 36. The method of claim 35, wherein the reactantis configured to effect a chemical reaction between the secondarymaterial and the reactant.
 37. The method of claim 27, wherein thepolymer includes at least one of polyvinylalanine, polystyrene, andpolycarbonate.
 38. The method of claim 27, wherein the secondarymaterial includes at least one of a phosphate glass and a silicateglass.
 39. A method for reinforcing a composite foam component, themethod comprising: providing a treatment mixture comprising a secondarymaterial and a solvent; and exposing a carbon foam material comprising anetwork of pores and a plurality of discontinuities to the treatmentmixture, wherein exposing the carbon foam material to the treatmentmixture effects a transfer of at least some of the secondary material tothe carbon foam material such that the secondary material is selectivelydeposited on or within at least some of the plurality of discontinuitiesin an amount of about 0.5 percent by weight or greater and less than 25percent by weight of the composite foam.
 40. The method of claim 39,wherein the solvent includes a substantially non-polar substance. 41.The method of claim 39, wherein the solvent includes at least one ofxylene and methylene chloride.
 42. The method of claim 39, wherein thecarbon foam material includes graphite foam.
 43. The method of claim 39,wherein the secondary material includes a polymer.
 44. The method ofclaim 43, wherein the polymer includes at least one of polyvinylalanine,polystyrene, and a polycarbonate.
 45. The method of claim 39, whereinthe secondary material includes at least one of a phosphate glass and asilicate glass.